1. Field of the Invention
This invention relates to a portable stormwater sediment filter which can be used adjacent to the street or curb inlet of a conventional storm drainage basin.
2. Description of the Prior Art
Unfiltered stormwater runoff is collected through the recessed curb or street inlets of storm sewer drainage basins. In large development sites, sediment laden stormwater is generated from construction erosion and is a major pollutant. Thus, builders and developers must meet, as part of the overall development plan, erosion control restrictions which require sediment removal at the curb inlet.
The prior art discloses sediment filters which combine cinder blocks, wire screen and gravel. Cinder block and gravel filters are constructed, in situ, by placing a single cinder block adjacent to the curbside at each end of the inlet throat projecting outwardly so that the hollow channel openings run parallel to the curbside. A 2.times.4 inch wood stud is placed adjacent to, and along the entire span of the inlet throat so that the ends of the wood stud are secured by extension through the hollow channels of the cinder blocks. Additional cinder blocks are then set end-to-end lengthwise against the wood stud along the full span of the inlet throat so that the hollow channels are capable of receiving a horizontal flow of unfiltered water. The wood stud thus serves to create an overflow gap between the inlet throat and the cinder blocks in order to prevent ponding and flooding. Wire screen is located around the perimeter of the cinder blocks in order to prevent movement of a coarse gravel filter medium piled around the perimeter of the wire screen. Unfiltered runoff permeates downstream toward the inlet throat through the gravel, for sediment removal, into the hollow channels of the cinder blocks, over the wood stud, and into the inlet throat of the sewer basin. During periods of high runoff volume, excess water pours over the gravel and cinder block assembly through the gap created by the wood stud. Filters constructed in this manner require technical ability in their construction, are hazardous because the assembly projects into the traffic flow, and necessitate frequent repair because the curbside gutter support is often nonhorizontal, causing the cinder blocks to tip or collapse into the inlet when subject to ponding or flooding conditions.
Another prior art design utilizes straw bales staked tightly within a 4 inch soil trench cleared around the perimeter of the inlet. The bales must be abutting with no gaps, and the trench is backfilled around the outside perimeter of the straw bales. Straw bale filters, however, cannot be used on a paved or concrete support surface, are easily damaged, and the assembly is labor intensive.
Sediment filters, with or without a dischargeable filtration media, have been described in certain U.S. patents. For example, Heggemier et al., U.S. Pat. No. 5,232,587, shows a planer filter resting on angle iron supports fixed inside of a storm sewer basin. A perforated aluminum sediment filter is riveted to a tubular steel frame, a weir and hydraulic opening for flow conveyance is provided adjacent to the filter and a grate-type rack is constructed across the hydraulic opening which serves as an overflow. Lutz, U.S. Pat. No. 809,201, discloses a removable wire basket sediment filter disposed inside an underground sewer basin. Unfiltered surface water passes through a vertical screened opening in order to remove sediment. A subsidiary screened outlet allows water to escape around the basket when the basket is full of sediment. Murfae, et al., U.S. Pat. No. 5,133,619, discloses a removable metal filter basket housed in a basin disposed in an alternative runoff path upstream from the stormwater receiving basin. The basket contains a dischargeable filtration media and lifting channels which enable the basket to be removed from the basin by the tines of conventional waste disposal vehicles. Designs of this type are of a permanent nature, costly to implement, require removal from the sewer basin for cleaning, and are not easily adopted to inlets of varying dimensions.